East Coast braces for rain and snow

The first day of winter is still about six weeks away but forecasters say the tempest dubbed Superstorm Sandy might be a preview of coming attractions during the next several months.

October was yet another month that was warmer than average, as Worcester Regional Airport recorded a monthly average temperature of 3 degrees above normal.

The beginning of November promises to be different, however, as today's earlier sunset, courtesy of pushing the clocks back an hour, is coming at the same time colder weather is arriving in Central Massachusetts.

Looming on the horizon is a coastal storm predicted by the National Weather Service that could start Wednesday as snow in the hilly areas of Central Massachusetts, before turning into a windswept, heavy rain that could deliver at least 2 inches.

Forecasters are worried that the nor'easter could cause more damage to the section of the East Coast that was ravaged last week by Sandy.

“This upcoming storm on its own isn't especially noteworthy. It should be an average nor'easter for November,” said Judah Cohen, principal scientist and director of seasonal forecasting for Lexington-based Atmospheric and Environmental Research, which is a Verisk Analytics company. “The fact that it comes so soon after Sandy makes it of more concern.”

Mr. Cohen has garnered news coverage in recent years because of research he has done on the connection between snow cover in Siberia and its effect on winter weather conditions in the United States.

Siberia and northern Canada are source regions for cold air that flows south and east toward the United States during the winter. Air that begins its trip toward the U.S. mainland from snow-covered ground that reflects warming sunlight skyward is colder than air that travels over snowless terrain that soaks up heat from the sun, according to forecasters.

“Snow cover there is more extensive than last year,” Mr. Cohen said

The colder air also helps change wind patterns, and mixes with warm air heading north from the equator, and the result can mean winter storms and cold weather.

The cold air remained bottled up in the far north last year, leading to one of the coldest winters ever in Alaska and one of the mildest in the eastern United States since records started.

“There was very little mixing last winter,” Mr. Cohen said. “It should be different this year.”

Well-known long-range winter weather forecaster Joseph S. D'Aleo, who is also co-chief meteorologist of Weatherbell.com, said this winter should be considerably colder than last winter, with the chance of at least one major winter storm.

AccuWeather.com is calling for slightly-above-average snowfall in Central Massachusetts, according to senior forecaster John L. Feerick.

Worcester Regional Airport averages slightly less than 70 inches of snow a year. Last year, the airport measured 38.5 inches of snow, with about a third of that falling during the memorable Oct. 29 snowstorm.

Mr. Feerick pointed to a high pressure system far to the northeast of Central Massachusetts, near Greenland, as playing a key role in forecasts for more snow this winter.

Mr. D'Aleo and Mr. Feerick said the high pressure area was so strong that it blocked Sandy from going out to sea as storms ordinarily do and forced it to crash into the New Jersey coast.

The blocking pattern, known to meteorologists as a negative North Atlantic oscillation, also plays a role in the formation of large East Coast storms such as the one that is expected to hit the area mid-week.

“It looks like it is going to be primarily rain for most of New England, although there could be some heavy snow in the mountains,” said Mr. D'Aleo. “But that's OK, it's only early November and we'll have other chances this winter.”

Mr. Cohen and Mr. D'Aleo said the negative NAO is still strong, although it is expected to weaken later this month before strengthening again next month, when Mr. D'Aleo expects a large storm to hit the area.

Mr. D'Aleo and Mr. Cohen said some of this winter's storms will go out to sea before reaching Central Massachusetts.

“But for people who like to keep track of storms and like snow, it should be an interesting winter,” he said.

Mr. D'Aleo said the blocking weather pattern that should occur at times in the upcoming winter means storms can stall off the East Coast and bring prolonged bouts of snow. He said his look ahead for the next few months shows the possibility of a storm like the one in February 1969 that brought occasional snow to Boston for four consecutive days.

Meanwhile, the National Oceanic and Atmospheric Administration's Climate Prediction Center says a weaker-than-expected El Niņo is making this winter's forecast less certain than in previous years. For example, the CPC's forecast calls for an average winter for the Northeast because there is no strong signal for either unusually cold or warm weather.

A strong El Niņo, which is a pronounced warming of the equatorial Pacific Ocean, can be the catalyst for strong storms in the United States.

“This is one of the most challenging outlooks we've produced in recent years because El Niņo decided not to show up as expected,” said CPC Deputy Director Michael Halpert in a press release.

Then there is the Old Farmer's Almanac, which said it correctly predicted last winter's abnormally lackluster winter. Its forecast calls for a colder, drier winter than normal, with less snowfall than average. Mr. D'Aleo agrees with the colder part but added he isn't as sure it will be less snowy than average.